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Homework 6: Hash Maps
Homework 6: Hash Maps
Important There are general homework guidelines you must always follow. If you fail to follow any of the following guidelines you risk receiving a 0 for the entire assignment. 1. All submitted code must compile under JDK 8. This includes unused code, so don’t submit extra files that don’t compile. Any compile errors will result in a 0. 2. Do not include any package declarations in your classes. 3. Do not change any existing class headers, constructors, instance/global variables, or method signatures. 4. Do not add additional public methods. 5. Do not use anything that would trivialize the assignment. (e.g. don’t import/use java.util.ArrayList for an Array List assignment. Ask if you are unsure.) 6. Always be very conscious of efficiency. Even if your method is to be O(n), traversing the structure multiple times is considered inefficient unless that is absolutely required (and that case is extremely rare). 7. You must submit your source code, the .java files, not the compiled .class files. 8. After you submit your files, redownload them and run them to make sure they are what you intended to submit. You are responsible if you submit the wrong files. Hash Maps In this homework, you will implement a key-value hash map with an external chaining collision policy. A hash map maps keys to values and allows O(1) average case lookup of a value when the key is known. This hash map must be resized to have a capacity of 2n + 1 where n is the current capacity when the table exceeds (greater than, not greater than or equal to) a load factor of 0.67. These values are provided as constants in the interface, and the constants should be used within your code. The table should not add duplicate keys, but duplicate values are acceptable. In the event of a duplicate key, replace the existing value with the new value. There are two constructors in HashMap.java. As per the javadocs, you should use constructor chaining to implement the no-arg constructor. Hash Functions You should not write your own hash functions for this assignment; use the hashCode() method (every Object has one). If this is a negative value, mod by table length first, then take the absolute value (it must be done in this order to prevent overflow in certain cases). External Chaining Your hash map must implement an external chaining collision policy. If the hash value of the key is occupied and the key is not already in the map, add the key to the front of the chain. Adding Items When adding a key/value pair to a hash map, add the pair to the chain in the correct position. Also remember that keys are unique in a hash map, so you must ensure that duplicate keys are not added. 1 Homework 6: Hash Maps Due: See T-Square Grading Here is the grading breakdown for the assignment. There are various deductions not listed that are incurred when breaking the rules listed in this PDF, and in other various circumstances. Methods: put 17pts remove 15pts get 10pts containsKey 10pts keySet 5pts values 5pts resizeBackingTable 8pts clear 5pts Other: Checkstyle 10pts Efficiency 15pts Total: 100pts Keep in mind that some functions are dependent on others to work, such as remove methods requiring the add methods to work. Also, the size function is used many times throughout the tests, so if the size isn’t updated correctly, many tests can fail. A note on JUnits We have provided a very basic set of tests for your code, in HashMapStudentTests.java. These tests do not guarantee the correctness of your code (by any measure), nor does it guarantee you any grade. You may additionally post your own set of tests for others to use on the Georgia Tech GitHub as a gist. Do NOT post your tests on the public GitHub. There will be a link to the Georgia Tech GitHub as well as a list of JUnits other students have posted on the class Piazza. If you need help on running JUnits, there is a guide, available on T-Square under Resources, to help you run JUnits on the command line or in IntelliJ. Style and Formatting It is important that your code is not only functional but is also written clearly and with good style. We will be checking your code against a style checker that we are providing. It is located in T-Square, under Resources, along with instructions on how to use it. We will take off a point for every style error that occurs. If you feel like what you wrote is in accordance with good style but still sets off the style checker please email Raymond Ortiz (rortiz9@gatech.edu) with the subject header of “CheckStyle XML”. Javadocs Javadoc any helper methods you create in a style similar to the existing Javadocs. If a method is overridden or implemented from a superclass or an interface, you may use @Override instead of writing Javadocs. Any Javadocs you write must be useful and describe the contract, parameters, and return value of the method; random or useless javadocs added only to appease Checkstyle will lose points. Exceptions When throwing exceptions, you must include a message by passing in a String as a parameter. The message must be useful and tell the user what went wrong. “Error”, “BAD THING HAPPENED”, and “fail” are not good messages. The name of the exception itself is not a good message. 2 Homework 6: Hash Maps Due: See T-Square For example: Bad: throw new IndexOutOfBoundsException("Index is out of bounds."); Good: throw new IllegalArgumentException("Cannot insert null data into data structure."); Generics If available, use the generic type of the class; do not use the raw type of the class. For example, use new LinkedList() instead of new LinkedList(). Using the raw type of the class will result in a penalty. Forbidden Statements You may not use these in your code at any time in CS 1332. • break may only be used in switch-case statements • continue • package • System.arraycopy() • clone() • assert() • Arrays class • Array class • Collections class • Collection.toArray() • Reflection APIs • Inner or nested classes • Lambda Expressions • Method References If you’re not sure on whether you can use something, and it’s not mentioned here or anywhere else in the homework files, just ask. Debug print statements are fine, but nothing should be printed when we run your code. We expect clean runs - printing to the console when we’re grading will result in a penalty. If you submit these, we will take off points. Provided The following file(s) have been provided to you. There are several, but you will only edit one of them. 3 Homework 6: Hash Maps Due: See T-Square 1. HashMapInterface.java This is the interface you will implement in HashMap. All instructions for what the methods should do are in the javadocs. Do not alter this file. 2. HashMap.java This is the class in which you will implement HashMapInterface. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance variables, or static variables. 3. MapEntry.java This class stores a key-value pair and a removed attribute for your hash map. Do not alter this file. 4. HashMapStudentTests.java This is the test class that contains a set of tests covering the basic operations on the HashMap class. It is not intended to be exhaustive and does not guarantee any type of grade. Write your own tests to ensure you cover all edge cases. Deliverables You must submit all of the following file(s). Please make sure the filename matches the filename(s) below, and that only the following file(s) are present. T-Square does not delete files from old uploads; you must do this manually. Failure to do so may result in a penalty. After submitting, be sure you receive the confirmation email from T-Square, and then download your uploaded files to a new folder, copy over the interfaces, recompile, and run. It is your responsibility to re-test your submission and discover editing oddities, upload issues, etc. 1. HashMap.java 4
Important There are general homework guidelines you must always follow. If you fail to follow any of the following guidelines you risk receiving a 0 for the entire assignment. 1. All submitted code must compile under JDK 8. This includes unused code, so don’t submit extra files that don’t compile. Any compile errors will result in a 0. 2. Do not include any package declarations in your classes. 3. Do not change any existing class headers, constructors, instance/global variables, or method signatures. 4. Do not add additional public methods. 5. Do not use anything that would trivialize the assignment. (e.g. don’t import/use java.util.ArrayList for an Array List assignment. Ask if you are unsure.) 6. Always be very conscious of efficiency. Even if your method is to be O(n), traversing the structure multiple times is considered inefficient unless that is absolutely required (and that case is extremely rare). 7. You must submit your source code, the .java files, not the compiled .class files. 8. After you submit your files, redownload them and run them to make sure they are what you intended to submit. You are responsible if you submit the wrong files. Hash Maps In this homework, you will implement a key-value hash map with an external chaining collision policy. A hash map maps keys to values and allows O(1) average case lookup of a value when the key is known. This hash map must be resized to have a capacity of 2n + 1 where n is the current capacity when the table exceeds (greater than, not greater than or equal to) a load factor of 0.67. These values are provided as constants in the interface, and the constants should be used within your code. The table should not add duplicate keys, but duplicate values are acceptable. In the event of a duplicate key, replace the existing value with the new value. There are two constructors in HashMap.java. As per the javadocs, you should use constructor chaining to implement the no-arg constructor. Hash Functions You should not write your own hash functions for this assignment; use the hashCode() method (every Object has one). If this is a negative value, mod by table length first, then take the absolute value (it must be done in this order to prevent overflow in certain cases). External Chaining Your hash map must implement an external chaining collision policy. If the hash value of the key is occupied and the key is not already in the map, add the key to the front of the chain. Adding Items When adding a key/value pair to a hash map, add the pair to the chain in the correct position. Also remember that keys are unique in a hash map, so you must ensure that duplicate keys are not added. 1 Homework 6: Hash Maps Due: See T-Square Grading Here is the grading breakdown for the assignment. There are various deductions not listed that are incurred when breaking the rules listed in this PDF, and in other various circumstances. Methods: put 17pts remove 15pts get 10pts containsKey 10pts keySet 5pts values 5pts resizeBackingTable 8pts clear 5pts Other: Checkstyle 10pts Efficiency 15pts Total: 100pts Keep in mind that some functions are dependent on others to work, such as remove methods requiring the add methods to work. Also, the size function is used many times throughout the tests, so if the size isn’t updated correctly, many tests can fail. A note on JUnits We have provided a very basic set of tests for your code, in HashMapStudentTests.java. These tests do not guarantee the correctness of your code (by any measure), nor does it guarantee you any grade. You may additionally post your own set of tests for others to use on the Georgia Tech GitHub as a gist. Do NOT post your tests on the public GitHub. There will be a link to the Georgia Tech GitHub as well as a list of JUnits other students have posted on the class Piazza. If you need help on running JUnits, there is a guide, available on T-Square under Resources, to help you run JUnits on the command line or in IntelliJ. Style and Formatting It is important that your code is not only functional but is also written clearly and with good style. We will be checking your code against a style checker that we are providing. It is located in T-Square, under Resources, along with instructions on how to use it. We will take off a point for every style error that occurs. If you feel like what you wrote is in accordance with good style but still sets off the style checker please email Raymond Ortiz (rortiz9@gatech.edu) with the subject header of “CheckStyle XML”. Javadocs Javadoc any helper methods you create in a style similar to the existing Javadocs. If a method is overridden or implemented from a superclass or an interface, you may use @Override instead of writing Javadocs. Any Javadocs you write must be useful and describe the contract, parameters, and return value of the method; random or useless javadocs added only to appease Checkstyle will lose points. Exceptions When throwing exceptions, you must include a message by passing in a String as a parameter. The message must be useful and tell the user what went wrong. “Error”, “BAD THING HAPPENED”, and “fail” are not good messages. The name of the exception itself is not a good message. 2 Homework 6: Hash Maps Due: See T-Square For example: Bad: throw new IndexOutOfBoundsException("Index is out of bounds."); Good: throw new IllegalArgumentException("Cannot insert null data into data structure."); Generics If available, use the generic type of the class; do not use the raw type of the class. For example, use new LinkedList() instead of new LinkedList(). Using the raw type of the class will result in a penalty. Forbidden Statements You may not use these in your code at any time in CS 1332. • break may only be used in switch-case statements • continue • package • System.arraycopy() • clone() • assert() • Arrays class • Array class • Collections class • Collection.toArray() • Reflection APIs • Inner or nested classes • Lambda Expressions • Method References If you’re not sure on whether you can use something, and it’s not mentioned here or anywhere else in the homework files, just ask. Debug print statements are fine, but nothing should be printed when we run your code. We expect clean runs - printing to the console when we’re grading will result in a penalty. If you submit these, we will take off points. Provided The following file(s) have been provided to you. There are several, but you will only edit one of them. 3 Homework 6: Hash Maps Due: See T-Square 1. HashMapInterface.java This is the interface you will implement in HashMap. All instructions for what the methods should do are in the javadocs. Do not alter this file. 2. HashMap.java This is the class in which you will implement HashMapInterface. Feel free to add private helper methods but do not add any new public methods, inner/nested classes, instance variables, or static variables. 3. MapEntry.java This class stores a key-value pair and a removed attribute for your hash map. Do not alter this file. 4. HashMapStudentTests.java This is the test class that contains a set of tests covering the basic operations on the HashMap class. It is not intended to be exhaustive and does not guarantee any type of grade. Write your own tests to ensure you cover all edge cases. Deliverables You must submit all of the following file(s). Please make sure the filename matches the filename(s) below, and that only the following file(s) are present. T-Square does not delete files from old uploads; you must do this manually. Failure to do so may result in a penalty. After submitting, be sure you receive the confirmation email from T-Square, and then download your uploaded files to a new folder, copy over the interfaces, recompile, and run. It is your responsibility to re-test your submission and discover editing oddities, upload issues, etc. 1. HashMap.java 4
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